Using the case of Ulaanbaatar, Erdenet, and Darkhan cities from Mongolia, the study aimed to assess the contamination level and health risk assessment of heavy metals (As, Cr, Pb, Ni, and Zn) in urban soil. A total of 78 samples was collected from a variety of functional areas. The geoaccumulation index (I_geo) and integrated pollution index (IPI) were used in pollution assessment, while the health risk was scored using a hazard quotient (HQ) and health index (HI) for non-carcinogenic heavy metals, as well as a lifetime average daily dose (LADD) for carcinogenic heavy metals. The results show that the concentration of heavy metals in the soil samples taken from Darkhan city, which presented “uncontaminated” values in terms of I_geo for all metals, was relatively lower than other cities within the contamination assessment. Furthermore, the I_geo value signified “uncontimated to heavily contaminated” soil in the Ulaanbaatar and Erdenet cities. Typically, as for the IPI that observed similar trends with I_geo, the mean IPI values in Ulaanbaatar, Erdenet, and Darkhan were 1.33 (moderate level of pollution), 1.83 (moderate level of pollution), and 0.94 (low level of pollution), respectively. In terms of the assessment of potential health risk, there was a particular or different level of ingestion, dermal contact, and inhalation exposure pathway for human health. Among these three different pathways, the ingestion was estimated by the main contributor for health risk. Each value of HQ and HI indicated that soil heavy metals of studied cities were at a safe level (<1) or had the absence of a significant health risk there. In addition, the potential health risk for children was greater than for adults, where heavy metal values of HI for children had a high value compared to adults. We estimated carcinogenic risks through the inhalation exposure, and as a result, there were no significant risks for human health in the studied cities from three elements (As, Cr, and Ni).

The purpose of this study was to identify pollution sources by characterizing polycyclic aromatic hydrocarbons from total suspended particles in Ulaanbaatar City. Fifteen polycyclic aromatic hydrocarbons were measured in total suspended particle samples collected from different sites, such as the urban center, industrial district and ger (Mongolian traditional house) areas, and residential areas both in heating (January, March), and non-heating (September) periods in 2017. Polycyclic aromatic hydrocarbon concentration ranged between 131 and 773 ng·m⁻³ in winter, 22.2 and 530.6 ng·m⁻³ in spring, and between 1.4 and 54.6 ng·m⁻³ in autumn. Concentrations of specific polycyclic aromatic hydrocarbons such as phenanthrene were higher in the ger area in winter and spring seasons, and the pyrene concentration was dominant in late summer in the residential area. Polycyclic aromatic hydrocarbons concentrations in the ger area were particularly higher than the other sites, especially in winter. Polycyclic aromatic hydrocarbon ratios indicated that vehicle emissions were likely the main source at the city center in the winter time. Mixed contributions from biomass, coal, and petroleum combustion were responsible for the particulate polycyclic aromatic hydrocarbon pollution at other sampling sites during the whole observation period. The lifetime inhalation cancer risk values in the ger area due to winter pollution were estimated to be 1.2 × 10⁻⁵ and 2.1 × 10⁻⁵ for child and adult exposures, respectively, which significantly exceed Environmental Protection Agency guidelines.

Most of the solid waste from Ulaanbaatar city during the cold season is ash from the partial combustion of coal. Burial of the ashes with other solid wastes has affected radioactive isotope levels in the soil. We investigated levels of radionuclides ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs in soil samples collected from the Naran Enger landfill using a gamma-ray spectrometer. The radioactivity of naturally occurring radionuclides in the soil samples was highest underneath the buried waste zone, and lowest around the ger areas and at the initial reference location. In the buried zone, activity of ⁴⁰K isotope was two times higher than the world average. The results showed that radium equivalent activity (Ra_eq) ranged between 69 and 183 Bq · kg⁻¹, and the Ra_eq of ash was 338.3 Bq · kg⁻¹. The external and internal hazard indexes were 0.2 and 0.5, respectively. From the Ra_eq, H_in, H_ex, D_out, and D_in values, we calculated lifetime cancer risk and found the risk to be (0.8−1.58) × 10⁻³. Current values of Ra_eq and hazard indices were found to be within the recommended limits.